Method of making mesoporous carbon

ABSTRACT

Mesoporous carbon and method of making involves forming a mixture of a high carbon-yielding carbon precursor that when carbonized yields greater than about 40% carbon on a cured basis, and an additive that can be catalyst metal and/or low carbon-yielding carbon precursor that when carbonized yields no greater than about 40% by weight carbon on a cured basis. When a catalyst metal is used, the amount of catalyst metal after the subsequent carbonization step is no greater than about 1 wt. % based on the carbon. The mixture is cured, and the carbon precursors are carbonized and activated to produce mesoporous activated carbon.

This application claims the benefit of U.S. Provisional Application Nos.60/074,241, filed Feb. 10, 1998, entitled “Mesoporous Carbon Bodies”, byKishor P. Gadkaree, and 60/093,396, filed Jul. 20, 1998, entitled“Method of Making Carbon Having Pore Size Distribution in the MesoporeRange”, by Gadkaree et al.

This invention relates to a method of making carbon of various poresizes, typically greater than 30 angstroms, from carbon precursors,utilizing low-yielding carbon precursors and/or suitable metal catalystcompounds. This ability to tailor pore size distribution is especiallyimportant for purification as well as catalytic applications.

BACKGROUND OF THE INVENTION

Activated carbon has found use in various applications such as air andwater purification, hydrocarbon adsorption in automotive evaporativeemission control and cold start hydrocarbon adsorption, etc. Whilemicroporous structure carbon (pore diameter less than 20 angstroms andBET surface area of 1000-3000 m²/g) are suitable for many applicationssuch as gas phase adsorption e.g. light hydrocarbons and H₂S, someapplications require larger size of pores in the carbon for optimumadsorption and/or catalytic activity. For example, removal of largermolecular size pollutants such as humine, protein, etc. in liquid phase,in addition to conventional gaseous pollutants, such as hydrocarbons, orcertain kinds of pesticides require specific surface properties andporesize distributions. When catalytic or chemical reaction is limitedby mass and heat transfer, larger size of pores in the carbon ispreferred. Also, mesoporosity in the carbon is sometimes required foradequate catalyst loading and dispersion.

Activated carbon monoliths, whether in the form of a coating on asubstrate, or a shaped structure of activated carbon, have found use invarious applications especially where durability and low pressure dropis required, such as some chemical reactions using strong acidic orbasic solvents or other corrosive media.

Metal catalysts have been used to make activated carbon supportedcatalysts, as have been disclosed in U.S. Pat. No. 5,488,023. However,up to this time, there has not been a method of making activated carbonthat having tailored properties, porosity, for example, for some gas andliquid phase, as well as catalytic applications.

SUMMARY OF THE INVENTION

In accordance with one aspect of the invention, there is providedmesoporous carbon and a method of making mesoporous carbon that involvesforming a mixture of a high carbon-yielding carbon precursor that whencarbonized yields greater than about 40% carbon on a cured basis, and anadditive that can be catalyst metal and/or low carbon-yielding carbonprecursor that when carbonized yields no greater than about 40% byweight carbon on a cured basis. When a catalyst metal is used, theamount of catalyst metal after the subsequent carbonization step is nogreater than about 1 wt. % based on the carbon. The mixture is cured,and the carbon precursors are carbonized and activated to producemesoporous activated carbon.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to making mesoporous activated carbon bycombining a high carbon-yielding carbon precursor, low carbon-yieldingadditive and/or catalyst metal compound followed by curing, carbonizingand finally activating the carbon by heat-treatment in activating agentssuch as steam and carbon dioxide, etc. When a catalyst metal compound isused, the amount of catalyst metal delivered is no greater than about 1%by weight based on the carbon that is present after the carbonizationstep.

According to this invention, by mesoporous carbon is meant that at leastabout 50%, and more typically about 60% to 90% of the total pore volumeis in the range of 20 to 500 angstroms and no more than 25 percent porevolume is in the range of large pores (>500 angstroms).

By carbon precursor is meant a synthetic polymeric carbon-containingsubstance that converts to continuous structure carbon on heating. Acarbon precursor is preferred over activated carbon particles because asa result of curing, carbonizing and activating, the carbon atoms arearranged in a continuous uninterrupted structure of randomthree-dimensional graphitic platelets.

By high-yielding carbon precursor is meant that on curing, the precursoryields greater than about 40% of the cured resin is converted to carbonon carbonization. For purposes of this invention, an especially usefulhigh-yielding carbon precursor is a synthetic polymeric carbonprecursor, e.g. a synthetic resin in the form of a solution or lowviscosity liquid at ambient temperatures or capable of being liquefiedby heating or other means. Synthetic polymeric carbon precursors includeany liquid or liquefiable carbonaceous substances. Examples of usefulcarbon precursors include thermosetting resins and some thermoplasticresins.

Low viscosity carbon precursors (e.g., thermosetting resins) arepreferred for coating applications because their low viscosity allowsgreater penetration into the substrate. Typical resin viscosity rangesfrom about 50 to 100 cp. Any high carbon yield resin can be used.Phenolic and furan resins are the most suitable. Phenolic resins aremost preferred due to their low viscosity, high carbon yield, highdegree of cross-linking upon curing relative to other precursors, andlow cost. Suitable phenolic resins are resole resin such as 43250polyophen resin, and 43290 from Occidental Chemical Corporation, andDurite resole resin from Borden Chemical Company. One especiallysuitable furan liquid resin is Furcab-LP from QO Chemicals Inc.

The carbon precursor can include a single high carbon-yielding precursormaterial, or a mixture of two or more such precursor materials.Optionally, already-made activated carbon can be added to liquid carbonprecursor to adjust the viscosity of the precursor for forming orshaping into structures.

To obtain carbon of desired porosity, a catalyst metal and/or lowcarbon-yielding carbon precursor is included with thehigh-carbon-yielding carbon precursor.

The low carbon-yielding carbon precursor is that which when carbonizedhas a carbon yield of no greater than about 40% on a cured basis. Someespecially useful low carbon-yielding carbon precursors are crosslinking additives are glycerine, melamine formaldehyde, epoxy, and/orpolyvinyl alcohol. One advantage of using the low carbon-yielding carbonprecursor alone without the catalyst metal is that the step of removingthe catalyst metal in cases where a catalyst metal is not desired in thefinal product, is eliminated.

When metal catalysts are present in the carbon matrix, topographicaleffects of surface etching, channeling and etch pitting are induced byeach individual metal additive during activation, depending on their ownphysical and chemical properties, carbon structures, and reactionconditions. To selectively generate desirable mesoporous activatedcarbon, these three actions are coordinated to provide desired poresize. Channeling and pitting provide a chance to produce pores, andsurface etching provides a chance for pore enlargement.

The metal catalyst suitable can be alkali, alkaline earth, transition,and/or noble metal. Advantageously, the catalyst metals are Pt, Pd, Rh,Ag, Au, Fe, Re, Sn, Nb, V, Zn, Pb, Ge, As, Se, Co, Cr, Ni, Mn, Cu, Li,Mg, Ba, Mo, Ru, Os, Ir, Ca, Y or combinations of these. Preferred metalsare Pt, Co, Ni, and/or Fe, especially Fe in the +3 oxidation state; withCo being especially preferred. The metal catalyst is preferably in theform of a precursor or compound e.g. organic or inorganic salt of acatalyst metal, which decomposes to the catalyst metal or catalyst metaloxide on heating, such as sulfates, nitrates, etc. A metal compound,preferably finely dispersed, is preferred to the elemental form becausemetal powder tends to form larger grains of graphitic regions instead ofthe favored opposite effect. Examples of compounds are oxides,chlorides, (except alkali or alkaline earths) nitrates, carbonates,sulphates, complex ammonium salts, etc. Organometallic compounds of theappropriate type metals can be used with or without low carbon-yieldingcarbon precursor. For example, acetates such as cobalt acetate, and/oracetylacetonates such as cobalt, platinum, and/or iron acetylacetonateare especially suited. While not wishing to be bound by theory, it isbelieved that the bulky organic structure introduced to the resin isthermally set after curing to the matrix and may help form more porositywhen these structures are removed during carbonization. Therefore, morecatalysts are exposed to the surface for additional pore sizeengineering during activation step.

The amount of metal catalyst used in the invention depends on the typeor activity of the metal catalyst, as well as the final porosity andpore size distribution desired, but is no greater than about 1%, andtypically from about 0.01% to 1%, and most typically about 0.01% to 0.2%by weight based on the carbon present after carbonization. For highlyactive Co, the concentration can be as low as 50 to 100 ppm. The amountof metal addition significantly affects the final pore structuresgenerated. Adding too much metal, however, will cause significantincrease in the metal sintering rate. The sintered particle tends toblock the pores and form the so-called bottle-necked pores. Also, whensintering happens, the activity of the catalysts drops and evendeactivates.

In some cases it is desirable to include both a catalyst metal and lowcarbon-yielding carbon precursor as the additives. For examplecombinations of cobalt e.g, cobalt acetate or nitrate and/or ironcompounds, e.g. iron nitrate, with the above cross-linking additives areuseful. Especially advantageous are combinations of cobalt acetate oriron acetylacetonate with glycerine and/or polyvinyl alcohol.

One useful method of making the mesoporous activated carbon is to coatan inorganic substrate such as a honeycomb with a coating suspension orsolution of the carbon precursor and the catalyst metal compound,followed by curing, carbonizing, and activating the carbon to form acontinuous coating of activated carbon. For example, about 7 g ofcatalyst precursor, Co(II) nitrate is first dissolved into a smallamount of water, and then put into 1000 ml of low viscosity phenolicresole resin. The mixture is homogenized to form a uniform solution. Thesuspension or solution is then coated onto a substrate, e.g. amonolithic substrate such as one made of cordierite. This is then curedat about 150° C., after drying at about 90-100° C., and then carbonizedand activated in activating agents such as carbon dioxide or steam.

The substrate has an outer surface from which pores extend into thesubstrate. The coating penetrates into and is distributed throughoutthese pores as a coating thereon.

In its most useful form the monolithic substrate has means for passageof a fluid stream therethrough, e.g., a network of pores communicatingfrom the outside to the inside, and/or through channels extending fromone end of the monolith to the other for passage of the fluid streaminto one end and out through the other end.

The substrate must have enough strength to function in the applicationand be capable of withstanding the heat-treating temperature experiencedin forming the activated carbon coating.

It is desirable that the overall open porosity of the substrate be atleast about 10%, preferably greater than about 25% and most preferablygreater than about 40%. For most purposes, the desirable range ofporosity is about 45% to about 55%. Preferably the pores of thesubstrate material create “interconnecting porosity” which ischaracterized by pores which connect into and/or intersect other poresto create a tortuous network of porosity within the substrate.

Suitable porous substrate materials include ceramic, glass ceramic,glass, metal, clays, and combinations thereof. By combinations is meantphysical or chemical combinations, e.g., mixtures, compounds, orcomposites.

Some materials that are especially suited to the practice of the presentinvention, although it is to be understood that the invention is notlimited to such, are those made of cordierite, mullite, clay, magnesia,and metal oxides, talc, zircon, zirconia, zirconates, zirconia-spinel,magnesium alumino-silicates, spinel, alumina, silica, silicates,borides, alumino-silicates, e.g., porcelains, lithium aluminosilicates,alumina silica, feldspar, titania, fused silica, nitrides, borides,carbides, e.g., silicon carbide, silicon nitride or mixtures of these.Cordierite is preferred because its coefficient of thermal expansion iscomparable to that of carbon, increasing the stability of the activatedcarbon body. Some typical ceramic substrates are disclosed in U.S. Pat.Nos. 4,127,691 and 3,885,977. Those patents are herein incorporated byreference as filed.

Suitable metallic materials are any metal or alloy or intermetalliccompound that provides durable structural service, and does not softenbelow about 600° C. Particularly useful are alloys that arepredominantly of iron group metal (i.e. Fe, Ni, and Co), either withcarbon (e.g. steels, especially stainless or high temperature steels) orwithout carbon. Most typical of the latter alloys for higher temperatureservice are those consisting essentially of iron group metal andaluminum, with the preferred iron group metal being iron. Especiallypreferred is Fe, Al, and Cr. For example, Fe5—20Al5—40Cr, andFe7—10Al10—20Cr powders with other possible additions are especiallysuited. Some typical compositions of metal powders for formingsubstrates are disclosed in U.S. Pat. Nos. 4,992,233, 4,758,272, and5,427,601 which are herein incorporated by reference as filed. U.S. Pat.Nos. 4,992,233 and 4,758,272 relate to methods of producing poroussintered bodies made from metal powder compositions of Fe and Al withoptional additions of Sn, Cu, and Cr. U.S. Pat. No. 5,427,601 relates toporous sintered bodies having a composition consisting essentially of inpercent by weight about 5 to 40 Cr, about 2 to 30 Al, 0 to about 5 ofspecial metal, 0 to about 4 of rare earth oxide additive and the balancebeing iron group metal and unavoidable impurities, with the preferrediron group metal being iron. When rare earth oxide is present, thespecial metal is at least one of Y, lanthanides, Zr, Hf, Ti, Si,alkaline earth metal, B, Cu, and Sn. When no rare earth oxide ispresent, the special metal is at least one of Y, lanthanide, Zr, Hf, Ti,Si, and B, with optional additions of alkaline earths, Cu, and Sn.

The substrate is preferably a honeycomb or matrix of thin walls forminga multiplicity of open-ended cells extending between the ends of thehoneycomb.

Generally honeycomb cell densities range from 235 cells/cm² (about 1500cells/in²) to 1 cell/cm² (about 6 cells/in²). Some examples of commonlyused honeycombs in addition to these, although it is to be understoodthat the invention is not limited to such, are about 94 cells/cm² (about600 cells/in²), about 62 cells/cm² (about 400 cells/in²), or about 47cells/cm² (about 300 cells/in²), and those having about 31 cells/cm²(about 200 cells/in²). Typical wall thicknesses are for example, about0.15 mm for about 62 cells/cm² (about 400 cells/in²) honeycombs. Wall(web) thicknesses range typically from about 0.1 to about 1.5 mm. Theexternal size and shape of the body is controlled by the application.

Cordierite honeycombs are especially preferred as substrates for themesoporous activated carbon.

The contacting is done by any method suitable to bring the carbonprecursor and metal catalyst in intimate contact with the inorganicsubstrate. Exemplary methods of contacting include dipping the substratein the carbon precursor(s) (with or without catalyst metal) solution orslurry, or spraying the carbon precursor(s) (with our without catalystmetal) solution or slurry directly on the substrate.

Another useful method of making the activated carbon with catalyst metalis to shape a mixture of the carbon precursor(s), (with or withoutcatalyst metal), binders and/or fillers, and forming aids, such as byextrusion.

Some binders that can be used are plasticizing temporary organic binderssuch as cellulose ethers. Some typical cellulose ethers aremethylcellulose, ethylhydroxy ethylcellulose, hydroxybutylcellulose,hydroxybutyl methylcellulose, hydroxyethylcellulose,hydroxymethylcellulose, hydroxypropylcellulose, hydroxypropylmethylcellulose, hydroxyethyl methylcellulose, sodium carboxymethylcellulose, and mixtures thereof. Methylcellulose and/ormethylcellulose derivatives are especially suited as organic binders inthe practice of the present invention with methylcellulose,hydroxypropyl methylcellulose, or combinations of these being preferred.

Some fillers that are suited include both natural and synthetic,hydrophobic, and hydrophilic, fibrous and non-fibrous, carbonizable andnon-carbonizable fillers.

For example some natural fillers are soft woods, e.g. pine, spruce,redwood, etc., hardwoods e.g. ash, beech, birch, maple, oak, etc.,sawdust, shell fibers e.g. ground almond shell, coconut shell, apricotpit shell, peanut shell, pecan shell, walnut shell, etc., cotton fiberse.g. cotton flock, cotton fabric, cellulose fibers, cotton seed fiber,chopped vegetable fibers for example, hemp, coconut fiber, jute, sisal,and other materials such as corn cobs, citrus pulp (dried), soybeanmeal, peat moss, wheat flour, wool fibers, corn, potato, rice, tapioca,coal powder, activated carbon powder, etc. Some synthetic materials areregenerated cellulose, rayon fabric, cellophane, etc.

Some examples of carbonizable fillers that are especially suited forliquid resins are cellulose, cotton, wood, and sisal, or combinations ofthese, all of which are preferably in the form of fibers.

Some inorganic fillers that can be used are oxygen-containing mineralssuch as clays, zeolites, talc, etc., carbonates, such as calciumcarbonate, aluminosilicates such as kaolin (an aluminosilicate clay),flyash (an aluminosilicate ash obtained after coal firing in powerplants), silicates, e.g. wollastonite (calcium metasilicate), titanates,zirconates, zirconia, zirconia spinel, magnesium aluminum silicates,mullite, alumina, alumina trihydrate, spinel, feldspar, attapulgites,and aluminosilicate fibers, cordierite powder, etc.

Some examples of especially suited inorganic fillers are cordieritepowder, talcs, clays, and aluminosilicate fibers.

Organic fillers provide additional support to the shaped structure andintroduce wall porosity on carbonization because in general they leavevery little carbon residue. Some organic fillers are polyacrylonitrilefibers, polyester fibers (flock), nylon fibers, polypropylene fibers(flock) or powder, acrylic fibers or powder, aramid fibers, polyvinylalcohol, etc.

Some binders and fillers that are especially suited are described inU.S. Pat. No. 5,820,967 filed May 20, 1996. That application is hereinincorporated by reference.

Some forming e.g. extrusion aids are soaps, fatty acids such as oleic,linoleic acid, etc., polyoxyethylene stearate, etc. or combinations ofthese. Especially preferred is sodium stearate. Optimized amounts ofextrusion aid(s) depend on the composition and binder.

The carbon precursor and metal catalysts (if present), mixed withcorrect amounts of the above-mentioned gradients are then subjected toheat-treatments to convert the carbon precursor to continuous carbon(carbonize).

The resulting carbon is then heat-treated to activate the carbon andproduce an activated carbon structure.

When the carbon precursor is a thermosetting resin, the carbon precursoris cured prior to activation and most typically prior to carbonization.The curing is accomplished typically by heating the precursor totemperatures of about 100° C. to about 200° C. for about 0.5 to about5.0 hours. Curing is generally performed in air at atmosphericpressures. When using certain precursors, (e.g., furfuryl alcohol)curing can be accomplished by adding a curing catalyst such as an acidcatalyst at room temperature. The curing also serves to retain theuniformity of the metal compound catalyst distribution in the carbon.

Carbonization is the thermal decomposition of the carbonaceous materialand embodied metal compound catalyst (if present), thereby eliminatinglow molecular weight species (e.g., carbon dioxide, water, gaseoushydrocarbons, etc.) and producing a fixed carbon mass and a rudimentarypore structure in the carbon.

Such conversion or carbonization of the cured carbon precursor isaccomplished typically by heating to a temperature in the range of about400° C. to about 800° C. for about 1 to about 10 hours in a reducing orinert atmosphere (e.g., nitrogen, argon, helium, etc.).

Curing and carbonizing the carbon precursor results in substantiallyuninterrupted carbon with uniformly dispersed catalyst particles (ifpresent) in carbon body. The catalyst usually is aggregated into largerparticles, different from the cured structures, where catalyst ismolecularly dispersed. The size of the catalyst particle depends on theamount added to the starting resin. The more catalyst in the initialresin, the easier the catalyst particle aggregates. The size of thecatalyst particle also depends on the carbonization and activationtemperature. Higher carbonization and activation temperatures inducesignificant metal sintering even when the metal concentration isrelatively low. Where the carbon is in the form of a coating, the carboncoating is anchored into the porosity of the substrate and as a resultis highly adherent. The top surface of the carbon coating is anuninterrupted layer of carbon to carbon bonds. If interconnectingporosity is present in the substrate, an interlocking network of carbonwill be formed within the composition, resulting in an even moreadherent carbon coating. The coating of uninterrupted carbon extendingover the outer surface of the substrate formed provides a structure withadvantages of high catalytic capability despite a relatively low carboncontent, high strength, and high use temperatures. Structures can beformed which contain carbon in an amount less than and up to about 50%often less than and up to about 30% of the total weight of the substrateand carbon.

Curing and carbonizing the catalyst metal compound in the carbonprecursor results in uniform and intimate chemical bonding of catalystwith uninterrupted carbon structure. The resulting catalyst particlesize, controlled by catalyst loading, process parameters, and nature ofcatalyst, etc., is a primary factor to determine pore sizes in theactivated carbon. Well-dispersed and uniform catalyst particle size canhelp to develop mesopores in the activated carbon in the latteractivation step.

The activation is done in a catalytic way to substantially create newporosity in the mesopore size range, as well as to enlarge the diameterof the micropores formed and therefore to increase the pore volume.Forming micropores without the assist of metal catalyst or the lowcarbon yielding carbon precursor according to this invention is usuallyinevitable. In general, activation can be carried out by standardmethods, in carbon dioxide or steam at about 400-900° C. If activationis in steam, the temperatures are preferably about 400° C. to about 800°C.

The lower carbonization and activation temperature is preferred whencarbonizing and activating catalyst-containing resins. At thecarbonization stage, a low temperature not only helps forming lesssintered large metal particles, but also contributes to forming arelatively less condensed carbon structure. Both factors are veryimportant for the subsequent pore generation during the activation step.For the same reason, a lower activation temperature is preferred. Fromthis point of view, steam activation is more preferred than carbondioxide activation, because of the lower temperature requirement ofsteam due to its higher reaction rates. The presence of a catalystprovides new catalytic active sites to start pore formation inactivation process instead of only carbon sites in non-catalyticactivation. The catalytic carbon activation reaction is faster thannon-catalytic carbon activation. Due to reaction rate difference betweencatalytic and non-catalytic modes, the catalytic activation becomesoverwhelmingly predominant over non-catalytic activation underactivation conditions. In addition, the presence of catalyst inducestopographical effects on pore formation during catalytic activation.Depending upon reaction conditions and nature of catalysts on the carbonsurface, pores greater than about 30 angstroms can be selectivelygenerated.

In accordance with one embodiment, the catalyst metal is Pt, e.g. in theform of dihydrogen chloroplatinic acid and the activation temperature isabout 650° C. to 750° C. in steam. Such conditions produce activatedcarbon having about 60% to 95% of the total porosity in the mesoporerange, and about 80 to 90% of the mesopore volume in the pore size rangeof about 40 to 300 angstroms.

In accordance with another embodiment, the catalyst metal is Co, e.g. inthe form of cobalt nitrate and the activation temperature is about 650°C. to 750° C. in steam. Such conditions produce activated carbon abouthaving 60 to 85% of the total porosity in the mesopore range, and about60 to 90% of the mesopore volume is in the pore size range of about 100to 400 angstroms.

In accordance with still another embodiment, the catalyst metal is Fe,particularly in the +3 oxidation state, e.g. in the form of iron nitratehexahydrate and the activation temperature is about 650° C. to 800° C.in steam. Such conditions produce activated carbon having about 80 to95% of the total porosity is in the mesopore range, and that about 85 to95% of mesopore volume is in the pore size range from 30 to 60angstroms.

Synthetic polymer-based carbon precursors, like phenolic resin typicallyforms hard carbon (also called char) with short-ranged graphiticmicrocrystalline structures after carbonization in inert atmosphere. Thechar that forms is very carbon-rich with a small amount of porosityproduced during removal of volatile products. While not wishing to bebound by theory, it is believed that the increase in pore sizes incarbon brought about by adding metal in the form of organo andinorgano-metallic compounds and activating the char using steam orcarbon dioxide is due to:

1) The increase in turbostratic nature of the resulting char even beforeactivation. In other words, the finely dispersed metal compounds promotethe formation of even more disordered structure during carbonizationthan would otherwise occur.

2) The metal compounds are reduced to the metallic state aftercarbonization. They are highly active and promote the activity of thecarbon in their vicinity. Larger pores are therefore generated aroundthe catalysts. Catalytic activation with the metal additivessignificantly increases the rate of activation. Moreover, the activationis carried out preferentially in the immediate vicinity of the metalparticles. As catalyst particles are pitting, channeling and surfaceetching through the carbon body, the size of pores formed (channels andpits) are equivalent or greater than the size of catalyst particles. Byadjusting catalyst particle size, the mesopores and even macropores canbe selectively produced.

3) Activation in steam is preferred to carbon dioxide. Steam produces awider porous texture, and a more mesoporous carbon and requires a muchlower temperature than CO₂.

Catalyst metals, if present, can be removed from the resultingmesoporous activated carbon body, or they can remain if they are neededin catalytic operations, etc. Removal is done by treating the body withan agent in liquid phase that will leach out the metal into solution andthe metal will then be washed away. Such agents are acids and bases,such as nitric, which will leach out most metals. Hydrochloric acidinstead of nitric acid works effectively for metals, which formcoordination compounds with the chloride such as platinum. Acetic acidcan be used for species that readily form acetates. If the carbonsurface is oxidized, as it may be if nitric acid or another oxidizingagent is used, it can be subjected to a subsequent treatment at elevatedtemperatures in nitrogen or hydrogen to produce a reduced surface.

The metal removal can also be done by treating the body with heat or anagent in gas phase that will form volatile metal compounds and theformed volatile compounds will release into gas phase by heating. Suchagents are carbon monoxide, hydrogen, and chlorine, etc. depending onnature of metal catalysts. Alkali metal can be directly removed fromcarbon body by heat treatment due to its high volatility. Metals likenickel, iron, cobalt, etc. can be removed through their volatilecarbonyl compounds formed with carbon monoxide.

To more fully illustrate the invention, the following non-limitingexamples are presented. All parts, portions, and percentages are on aweight basis unless otherwise stated.

Catalyst Metal Examples EXAMPLE 1

(Comparative)

Low viscosity phenolic resin about 100 to 150 cp was dip-coated ontoceramic cordierite honeycombs having about 50% open porosity. They werethen dried at 95° C., cured at 150° C., carbonized at 750° C. in N₂ andactivated in CO₂ at 900° C. for various time periods. Percent pores ineach of the three ranges were determined on a volume basis using N₂adsorption. The percent pore volume in the micropore range wasdetermined using the standard t-method. Percent mesopore volume wasdetermined using the BJH method. The resultant activated carbons featuremainly the characteristics of microporous carbons. Greater than about80% of pore volume is in the micropore range. Surface areas are at leastabove 1000 m²/g carbon. Although as the level of burn-off on activationincreases, the percent of mesopores increases slightly, the magnitude ofincrease is small compared to the level of carbon being burned-off.Conventional activated carbon manufacturing tends to producepredominantly microporous carbon, regardless of how high the burn offcan be. Surface area did increase significantly with the level ofburn-off. The pore size distributions tend not to change much with theincreasing of burn-off. In the burn-off range of the example, activationis a steady state carbon removal reaction.

EXAMPLE 2

Inventive

Ferric nitrate was used as the catalyst metal. About 7 g of ferricnitrate was added to a small amount of water. After it was completelydissolved, it was mixed into about 1000 ml of phenolic resole resin(same resin as above) and stirred vigorously to ensure homogeneousdispersion of the catalyst precursor. The metal containing mixture wasdip-coated using a cordierite honeycomb that had about 50% openporosity, and then dried at about 95° C. and cured at about 150° C.,carbonized at about 750° C. for about 1 hr in N₂, and activated at about700° C. for a period of 1 to 4 hours in steam and nitrogen mixture. Theresulting sample of activated carbon was analyzed using N₂ adsorptionisotherm for pore size distribution. The resulting activated carbon ismainly mesoporous, the mesoporous content being 80-90% of the totalporosity. The carbon has about 10% of micropores and macropores. Themajority of pores in the mesopore range is around 30 to 60 angstroms(85% of mesopores) with a peak at 38 angstroms. The surface area of themesoporous carbon ranges from 500 to 650 m²/g carbon.

There is a significant drop in the total surface area in thecatalyst-assisted activation, indicating the presence of larger pores.The amount of microporosity dropped significantly with the addition ofcatalysts. The amount of mesoporosity tends to increase with the levelof carbon burn-off. The Fe-containing carbon produced a mesoporouscarbon with a peak around 38 angstroms in the mesopores range.

EXAMPLE 3

Inventive

Cobalt nitrate was used as the catalyst metal. About 7.0 g Co was used,following the same procedure as Example 2. The resulting activatedcarbon has around 70 to 80% mesopore and 20 to 25% macropore content.The surface areas range from 450 to 550 m²/g carbon. Cobalt-containingcarbon produced a bi-modal distribution in the mesopore range, withpeaks centered around 38 and 250 angstroms.

EXAMPLE 4

Inventive

The procedure of Example 2 was followed, except that the metal compoundsadded were reduced to about 2.8 grams, also the activations wereconducted at 700° C. in steam and nitrogen mixture. The resultantactivated carbon has 60% mesopores and 25% macropores, with a surfacearea of around 600 m²/g. This carbon also has a single peak in themesopore range at 250 angstroms. The size of the peak is such that about75% of the mesopore volume was in the pores ranging from 100 to 400angstroms.

EXAMPLE 5

Inventive

Dihydrogen chloroplatinic acid (CPA) was used as catalyst metal. About 5g of CPA was added following the same procedure of Examples 2 and 3. Theresultant activated carbon has about 70% mesopore and 10% macroporecontent, with a surface area close to 550 m²/g. This carbon has acharacteristic peak in the mesopore range centered at 100 angstroms. Thesize of the peak is such that about 80% of the mesopore volume was inthe pores ranging from 40 to 300 angstroms.

EXAMPLE 6

Comparative

Phenolic resole resin from Occidental Chemical Co., Niagara Falls, N.Y.was coated onto a cordierite honeycomb and then dried at about 90° C.,cured at about 125-150° C., and carbonized in nitrogen at about 900° C.and activated in carbon dioxide at about 900° C. The pore sizedistribution of the resulting carbon was measured on Micrometrics(norcross, Ga.) ASAP 2000 equipment via measurement of nitrogenadsorption isotherm. Carbon is essentially all microporous with all thepores in the 10 angstrom or lower range.

EXAMPLE 7

Inventive

Example 6 was repeated except that to the resin, about 1% iron acetylacetonate was added before coating. The coated honeycomb was cured,carbonized, and activated in carbon dioxide. About 60% of the ofmesopores present have a mean pore size of about 90 angstroms.

EXAMPLE 8

Comparative

An extruded resin honeycomb was fabricated by mixing about 55.6%phenolic resole from Borden, Inc. with about 14.7% cordierite grog,about 22.2% cellulose fiber, about 2% phosphoric acid, about 4.6%Methocel®, and about 0.9% sodium stearate. The mixture was extruded andthen the resulting honeycomb was dried at about 90° C., cured,carbonized, and activated at about 900° C. in carbon dioxide. The poresize distribution shows essentially all microporous carbon with a meanpore size of about 5 angstroms and little or no mesoporosity.

EXAMPLE 9

Inventive

The experiment of Example 8 was repeated but with about 1% cobaltacetate added to the resin prior to mixing. The sample was processed asin Example 8. The pore size distribution shows 70% volume at about 400angstroms.

EXAMPLE 10

Inventive

The procedure of Example 6 was repeated, but to the resin was addedabout 50% glycerine and about 1% cobalt acetate based on the totalcoating liquid. On coating and processing as in Example 6, the pore sizedistribution shows about 70% mesopore volume with a mean pore size ofabout 500 angstroms. Only about 20% of the volume is in the microporerange.

EXAMPLE 11

Inventive

In an experiment similar to that of Example 10, about 20% polyvinylalcohol was added to the phenolic resole and then about 1% cobaltacetate was added before coating. The sample was processed as in Example6, and the pore size distribution showed about 69% of the volume in themesopore range and about 33% in the micropore range.

EXAMPLE 12

Inventive

About 34% melamine formaldehyde was added to the resin and the procedureof Example 11 was repeated. The pore size distribution showed about 50%of the pores in the mesopore range with a mean mesopore size of about 70angstroms.

Examples 6-12 above show that either by adding an iron or cobalt salt orcross linking additive such as glycerine, melamine formaldehyde, orpolyvinyl alcohol, the pore size distribution can be modified to obtainlarge pores, e.g. larger than about 50 angstroms, which otherwise do notform in phenolic resole based carbon.

EXAMPLE 13

(Comparative)

A batch containing Durite liquid phenolic resin from Borden, Inc. atabout 55.5%, cellulose fiber BH40 at about 22.2%, cordierite grog atabout 14.7%, Methocel® at about 4.7%, sodium stearate at about 0.9%, andphosphoric acid at about 2% was mixed in a muller and then extruded intoa honeycomb shape with about 400 cells/in.² and a wall thickness ofabout 12 mils. The sample was then dried at about 90° C. and then curedat about 125-150° C. Carbonization was carried out in nitrogen at about900° C. for about 6 hours and activation was carried out in carbondioxide at about 850° C. for about 4 hours. The pore size distributionof the resulting honeycomb is in the range of about 2-20 angstroms. Nopores larger than 20 angstroms are present.

EXAMPLE 14

(Inventive)

To the batch of Example 13, cobalt acetate at about a 1% level wasadded. The sample was then cured, carbonized, and activated in carbondioxide at about 750° C. for about 4 hours. The temperature ofactivation was reduced because cobalt promotes gasification of carbonand at about 850° C. very high uncontrolled burnoff takes place. Thereis a large volume of pores in the 50-110 angstrom range proving thatmesoporous carbon honeycombs can be made utilizing catalysts.

Such mesoporous bodies e.g. honeycombs are useful as catalyst supportsin chemical or petrochemical reactors or for adsorption or waterpurification applications.

EXAMPLE 15

Comparative

About 16.59 g nickel nitrate was first dissolved into 50 ml of water andthen mixed into about 1000 ml of phenolic resole resin. This high metalcontent resin was used for dip coating to make carbon-coated honeycombsaccording to a procedure similar to example 2. The metal content in thefinal carbon amounted to higher than 1 wt %. The final porous carbon hasa pore size distribution of 37% micropore, 28% mesopore, and 35%macropore. Significantly more large pores are produced as a result ofhigh catalyst metal content.

It should be understood that while the present invention has beendescribed in detail with respect to certain illustrative and specificembodiments thereof, it should not be considered limited to such but maybe used in other ways without departing from the spirit of the inventionand the scope of the appended claims.

What is claimed is:
 1. A method of making activated carbon having atleast about 50% of the total pore volume in the range of 20 to 500angstroms, and not more than 25% of the total pore volume in the rangeof greater 500 angstroms, the method comprising: a) forming a mixturecomprising a high carbon-yielding carbon precursor that when carbonizedyields greater than about 40% carbon on a cured basis, and an additiveselected from the group consisting of a low carbon-yielding carbonprecursor, selected from the group consisting of glycerin, melamineformaldehyde and epoxy, and a combination of a catalyst metal and saidlow-carbon yielding carbon precursor wherein said catalyst metal isselected from the group consisting of iron and cobalt, and wherein thecatalyst metal after the subsequent carbonization step is no greaterthan about 1 wt. % based on the carbon; b) curing the mixture; c)carbonizing the carbon precursors in the mixture; d) activating thecarbon to produce activated carbon having at least about 50% of thetotal pore volume in the range of 20 to 500 angstroms, and not more than25% of the total pore volume in the range of greater 500 angstroms; ande) removing said metal catalyst when said metal catalyst is used incombination with said low-carbon yielding precursor as an additive instep a).
 2. A method of claim 1 wherein the high carbon-yielding carbonprecursor is a thermosetting resin.
 3. A method of claim 2 wherein saidhigh carbon-yielding carbon precursor is phenolic resin.
 4. A method ofclaim 1 wherein the amount of catalyst metal is about 0.01% to 0.2% byweight based on the carbon.
 5. A method of claim 1 wherein the carbonprecursor and additive mixture is applied as a coating on a substrate.6. A method of claim 5 wherein the substrate is a honeycomb.
 7. A methodof claim 1 wherein the carbon precursor and the additive mixture iscombined with binders and shaped into a body.
 8. A method of claim 7wherein the shaping is done by extrusion.
 9. A method of claim 8 whereinthe carbon precursor, additive, and binder are extruded into ahoneycomb.
 10. A method of claim 1 wherein the activation is carried outin an atmosphere selected from the group consisting of steam, and carbondioxide.
 11. A method of claim 10 wherein the activation is carried outin steam.
 12. A method of claim 11 wherein the activation temperature isabout 400° C. to 800° C.